Response of Split-Root Sour Orange Seedlings to NaCl and Polyethylene Glycol Stresses

Soil water cotent and salinity levels are seldom uniform inthe field, particularly with the use of micro-irrigation systemsthat may water only a portion of the root zone. For studyingnon-uniform salinity, a split-root experiment was designed toevaluate growth and water relations when half of the root systemof sour orange (Citrus aurantium) seedlings was stressed withsodium chloride (NaCl) or polyethylene glycol (PEG). This studyalso determined if non-stressed portions of the root systemcompensated for the decrease in water uptake by the stressedportions. One or both halves of the root system were treated for fourmonths with nutrient solution adjusted with NaCl or PEG to osmoticpotentials of –0.10, –0.20, or –0.35 MPa.Shoot dry weight was reduced by only 9% when half of the rootsystem was irrigated with saline solution at –0.10 MPa,but with both halves of the root system at –0.10 MPa,shoot and root dry weights were reduced as much as 45%. Similarly,leaf water and osmotic potentials were also more disturbed underuniform salinity than under non-uniform salinity conditions. Plant growth, leaf water potential, osmotic potential, stomatalconductance, and evapotranspiration decreased with increasingNaCl and PEG concentrations in the nutrient solution. Turgorpotential and leaf thickness increased in response to NaCl treatments.Microscopic examination showed that the increase in leaf thicknesswas due to the development of larger cells in the spongy mesophyll. Shoot growth did not correlate with the average osmotic potentialof the two root halves. Seedlings with one stressed half-rootsystem had shoot dry weight and leaf water potential valuescloser to those of the non-stressed control than to those withthe completely stressed root system. Key words: Non-uniform salinity, water relations, citrus     

外生菌根真菌对重金属铜镉污染土壤中油松生长和元素积累分布的影响

该实验选取处于生长期的油松(Pinus tabulaeformis)幼苗,研究土壤Cu、Cd胁迫条件下,美味牛肝菌(Boletus edulis)单独接种、红绒盖牛肝菌(Xerocomus chrysenteron)与美味牛肝菌混合接种处理,对油松幼苗的生长和重金属积累分布状况的影响,探讨不同接种对油松抗性的影响。研究发现,菌根接种不仅促进寄主油松的生长发育和生物量积累,而且显著降低油松体内的重金属积累浓度,减少重金属由根部向植物茎叶部分的转运。与单一接种相比,混合接种可以更加有效地缓解重金属对寄主的生物毒性,减少土壤中重金属元素向油松体内的转运。这种优势在高浓度的重金属胁迫环境下尤为明显。该实验中,在3 mg·kg^-1 Cd胁迫下,混合菌根油松的茎叶和根部Cd浓度仅为未接种对照的59.1%和70.7%,比单一菌根降低了11.3%和18.1%,而混合菌根植物的茎叶和根部生物量干重则分别为未接种对照的1.14和1.20倍,单一菌根为未接种对照的1.18和1.17倍。在400 mg·kg^-1Cu胁迫下,混合菌根植物茎叶和根部的干重分别是未接种植株的1.01和1.09倍,而混合菌根植物茎叶和根部的Cu浓度仅为未接种植株的61.8%和79.6%,比Boletus edulis菌根植物的Cu积累浓度下降了0.7%和3.8%。     

Nutrient-limited growth rates: quantitative benefits of stress responses and some aspects of regulation

Young sunflower plants (Helianthus annuus L.) under stress oflow nitrate or phosphate availability exhibited increases inroot: shoot ratio and in kinetic parameters for uptake. Theyshowed no significant changes in photosynthetic utilizationof either nutrient. Increases in root: shoot ratio were achievedby early and persistent suppression of shoot growth, but notroot growth. Affinity for phosphate uptake, 1/K_m(P), increasedwith phosphate stress, as did affinity for nitrate uptake, 1/K_m(N),with nitrate stress. Maximal uptake rate, V_max, for phosphateuptake increased with phosphorus stress; V_max for nitrate didnot increase with nitrogen stress. Phosphate V_max was relatedstrongly to root nutrient status. Decreases in V_max with plantage were not well explained by changes in age structure of roots.Estimated benefits of acclimatory changes in root: shoot ratioand uptake kinetics ranged up to 2-fold increases in relativegrowth rate, RGR. The relation of RGR to uptake physiology followedpredictions of functional balance moderately well, with somesystematic deviations. Analyses of RGR using growth models implyno significant growth benefit from regulating Vmax, specifically,not from down-regulating it at high nutrient availability. Quantitativebenefits of increases in root: shoot ratio and uptake parametersare predicted to be quite small under common conditions whereinnutrient concentrations are significantly depleted by uptake.The root: shoot response is estimated to confer the smallestbenefit under non-depleting conditions and the largest benefitunder depleting conditions. Even then, the absolute benefitis predicted to be small, possibly excepting the case of heterogeneoussoils. Depleting and non-depleting conditions are addressedwith very different experimental techniques. We note that atheoretical framework is lacking that spans both these cases,other than purely numerical formulations that are not readilyinterpreted. Key words: Nutrient stress, nutrient uptake, nutrient use efficiency, relative growth rate, Helianthus annuus     

The Effects of Infection by Rust (Puccinia lagenophorae Cooke) on the Growth of Groundsel (Senecio vulgaris L.) Cultivated under a Range of Nutrient Concentrations

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae Cooke, was grown at a rangeof nutrient concentrations in sand culture. There were statisticallysignificant interactions between the effects of infection andnutrient supply upon the dry weights of stems, leaves, rootsand reproductive tissues, leaf area and cumulative capitulumproduction. This interaction occurred since infection causedsignificant inhibitions of growth only at moderate or high nutrientconcentrations. At low concentrations rusted plants were similarto or slightly larger than controls. Both in controls and rustedplants root: shoot ratios increased as nutrient supply declined.The ratio of root: shoot dry weight was consistently reducedby infection whilst root length: leaf area ratio was relativelyunchanged. More detailed investigations confirmed that infection had littleeffect on plant growth under nutrient deficient conditions despitesuppression of the host's ability to increase root: shoot ratiosin response to nutrient stress. This reflected the inhibitionof relative growth rates in rusted plants at high but not lownutrient concentrations, which in turn reflected reduced netassimilation rates (NAR). Increases in leaf-area ratio (LAR)often ameliorated the decline in NAR in rusted plants. Senecio vulgaris L., Puccinia lagenophorae Cooke, nutrient deficiency, growth, root: shoot ratio     

The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. in Flowing Solution Culture: I. GROWTH

Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. in flowing solution culture. I. Growth.—J.exp. Bot. 38: 42–52 Oilseed rape (Brassica napus L. cv. Bien venu) was grown for49 d in flowing nutrient solution at pH 6?0 with root temperaturedecrementally reduced from 20?C to 5?C; and then exposed todifferent root temperatures (3, 5, 7, 9, 11, 13,17 or 25?C)held constant for 14 d. The air temperature was 20/15?C day/nightand nitrogen was supplied automatically to maintain 10 mmolm^–3 NH₄NO₃ in solution. Total dry matter production wasexponential with time and similar at all root temperatures givinga specific growth rate of 0?0784 g g^–1 d^–1. Partitioningof dry matter was influenced by root temperature; shoot: rootratios increased during treatment at 17?C and 25?C but decreasedafter 5 d at 3?C and 5?C. The ratio of shoot specific growthrate: root specific growth rate increased with the ratio ofwater soluble carbohydrates (shoot: root). Concentrations ofwater soluble carbohydrates in shoot and root were inverselyrelated to root temperature; at 3, 5 and 7?C they increasedin stem + petioles throughout treatment, coinciding with a decreasein the weight of tissue water per unit dry matter. These resultssuggest that the accumulation of soluble carbohydrates at lowtemperature is the result of metabolic imbalance and of osmoticadjustment to water stress. Key words: Brassica napus, oilseed rape, root temperature, specific growth rate     

An Extension of the Logistic Model of Plant Growth

The kinetics of growth of Dactylis glomerata L. were studiedunder controlled temperature and nutritional conditions at threelevels of irradiance (35·55 and 85 W m^–s). Thedry weights of the root and shoot parts of the plants were measuredeach week between the fourth and eleventh weeks after sowing. The growth kinetics were found to be dependent on the levelof irradiance, but no significant differences in the root: totaldry weight ratio were observed. To characterize the effect of illuminance, the experimentalgrowth curves were analysed initially using the logistic model,the adequacy of which is discussed. An extension of the logisticmodel is proposed, represented by the kinetic equation dM/dt= kM, with < 1 and where M is the dry weight of the plant.It is shown that this relationship allows a distinction to bemade between two kinds of plant material according to theirfunctions in the growth process. Dactylis glomerata L., illuminance, growth curves, kinetic analyses, logistic model, shoot:root ratio, partition of assimilates     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Soybean growth on fly ashamended strip mine spoils

Summary The use of fly ash as an amendment for strip mine soils has been studied under field conditions. Spoils ranging in pH from 4.0–6.0 were tested. The addition of fly ash in all cases was effective as an acid soil neutralizer and substantially enhanced the growth and development of all experimental plants. The parameters used in growth analyses were plant height, dry weight, root/shoot ratios, nodulation, pod production, and nitrogen fixing capacity for legumes. re]19761004     

Morphological Changes in Wheat Seedlings (Triticum aestivum L.) following Root Anaerobiosis and Partial Pruning of the Root System

Morphological changes of roots and shoots following oxygen deficiencyin the root medium and after partial pruning of the root systemwere analyzed to obtain easily measurable parameters of theadaptive capacity of the root system against stress. Wheat seedlings(Triticum aestivum L. cv. Hatri) were cultivated on nutrientsolution which was either aerated or flushed with nitrogen,or were cultivated on flooded sand. On the third day after grainswelling in two pruning variants, roots 1–3 or 4–8were excised. Root anaerobiosis retarded longitudinal growth and biomass accumulationof the shoot and the seminal roots, and stimulated the developmentof adventitious roots. Partial removal caused a general compensativegrowth of the remaining roots under aerobic conditions. Root pruning plus anaerobiosis exceeded the compensatory capacityof the seedlings and thus caused a strong delay of elongationand biomass accumulation of both roots and shoots, includingdecrease of the root/shoot ratio. Roots became independent ofendosperm reserves on the seventh day under aerobic conditionsthough caryopses were not completely exhausted at this time.Additionally, oxygen deficiency delayed the reserve exhaustionprocess. Triticum aestivum L. cv Hatri, wheat, roots, growth analysis, morphology, anaerobiosis, strees, root pruning, compensatory capacity, caryopsis     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum. Growth, Ion and Water Relations and Gas Exchange in Response to Altered Salinity

Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaedamaritima L. Dum. Growth, ion and water relations and gas exchangein response to altered salinity.—J. exp. Bot. 38: 1996–2004. Shoot and root fresh and dry weights and shoot sodium, chlorideand potassium contents were measured and shoot relative growthrates calculated in seedlings of Suaeda maritima over a periodof 11 d following a raising of culture solution salinity from0 to 200 mol m₃– NaCl. Growth, growth rates and sodiumand chloride contents, as compared to plants growing in theabsence of salt were increased whilst potassium contents declined.Shoot sodium accumulation rate and the rate of transport ofsodium from root to shoot, osmotic potential, and rates of photosynthesisand transpiration were also measured for up to 72 h after transferof plants originally growing at 0 and 200 mol₃– NaCl to200 and 400 mol m₃– NaCl respectively. Ion uptake andtransport rates were maximal 6-12 h after transfer and thendeclined to new steady-state levels within 48 h; osmotic potentialswere lowered over a 72 h period on average by approximately1·0 MPa; and after 9 h photosynthetic and transpirationrates were reduced by about 20percnt; and 30% respectively.Results are discussed in terms of the ability of halophytesto adjust to fluctuating salinity and to salt tolerance mechanismsin general. Key words: Suaeda maritima, salinity, gas exchange, growth, ion and water relations     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

The Effects of Rootzone Salinity and Hypoxia on Shoot and Root Growth in Trifolium Species

The effect of concurrent salinity (0-60 mM NaCl) and rootzonehypoxia (flooding for up to 15 d) on shoot and root growth andshoot ion concentrations of six species of Trifolium (T. subterraneumL., T. fragiferum L., T. michelianum Savi., T. isthmocarpumBot., T. purpureum Lois., and T. repens L.), was studied intwo greenhouse experiments. There was a significant salinityx flooding effect for shoot yield but no significant salinityx flooding x species interaction although individual speciesdiffered significantly (P < 0·001) in their growthresponse to the saline or flooded conditions separately. Concentrationsof Na and Cl in the shoots of all species increased with increasingperiods of saline flooding and there was a significant salinityx flooding interaction. Sodium and Cl concentrations were significantlyhigher (P < 0·001) in T. purpureum, the species inwhich shoot growth was most depressed by saline flooding, thanother species. In T. michelianum, T. fragiferum and T. repens,fresh and dry weight of roots increased with flooding underboth saline and non-saline conditions while in T. subterraneumroot growth decreased. A significant proportion of the increasedroot growth in the first three species occurred as new adventitiousroots. These roots had higher percentages of internal gas spaceswithin the root tissue even in the presence of salinity comparedwith roots from non-flooded conditions. There were also significantlymore gas spaces in the total root tissue in T. fragiferum andT. repens under saline-flooding than in roots of T. subterraneum.Electron micrographs of the root cross sections illustratedthe presence of these gas spaces or aerenchyma. Trifolium fragiferum, T. repens and T. michelianum are morelikely to be suited to growth in soils prone to high salinityand to flooding than are T. subterraneum, T. purpureum and T.ishmocarpum.Copyright 1993, 1999 Academic Press Trifolium subterraneum, Trifolium fragiferum, Trifolium michelianum, Trifolium isthmocarpum, Trifolium purpureum, Trifolium repens, salinity, flooding, hypoxia, adventitious roots, aerenchyma, subterranean clover, white clover, strawberry clover, purple clover, balansa clover     

Differential Inhibition of Shootvs.Root Growth at Low Temperature and its Relationship with Carbohydrate Accumulation in Different Wheat Cultivars

Shoot and root growth rate, carbohydrate accumulation (includingfructan), reducing sugar content and dry matter percentage weremeasured in six wheat cultivars, ranging from winter to springtypes, grown at either 5 or 25 °C. At 5 °C (comparedwith 25 °C), the relative growth rate (RGR) of shoots wassimilarly reduced in all cultivars, but the RGR of shoots wasmore affected in winter wheats. This difference resulted insmaller root:shoot ratios than in spring wheats, which alsodeveloped more first-order lateral roots. A direct relationshipbetween carbohydrate accumulation at low temperatures and reductionin root growth was established. These results suggest that differentialshootvs.root growth inhibition at low temperature may play akey role in carbohydrate accumulation at chilling temperatures.This differential response might lead to improvements in survivalat temperatures below 0 °C, regrowth during spring, andwater and nutrient absorption at low temperatures.Copyright1997 Annals of Botany Company Wheat; Triticum aestivum; low temperatures; root growth; root: shoot ratio; sugar accumulation     

The Effect of Mechanically Induced Stress on the Growth of Cauliflower, Lettuce and Celery Seedlings

Brushing cauliflower, lettuce and celery seedlings with paperfor 1.5 min each day for 11–13 d, 10–12 d or 21–28d, respectively resulted in smaller, more compact, plants thanthe unbrushed controls. In all three species shoot fresh anddry weights and leaf area were reduced following brushing. Incauliflower and celery the largest growth reduction was in petiolelength. In lettuce, which has no discernible petioles, the reductionin leaf length caused by brushing was proportionally greaterthan the reduction in leaf width. Brushing reduced hypocotyllength in cauliflowers and to a lesser extent in lettuce. Petioleand hypocotyl thickness was reduced in cauliflower, whereashypocotyl thickness was increased in lettuce following brushing.Brushing increased leaf thickness in cauliflower, celery andto a lesser extent in lettuce and increased the percentage drymatter content of lettuce shoots. The weight of chlorophyllper fresh weight of leaf tissue increased following brushingin celery and lettuce and declined in cauliflowers. Root length and the number of branches per root system werereduced in all three species following brushing. Root dry weightwas reduced and the root:shoot dry weight ratio was increasedin lettuce, reduced in celery and unaffected in cauliflowers. There were different patterns of response to brushing, the reductionin leaf weight being greatest in the youngest leaf of cauliflowerand least in the youngest leaf of lettuce and celery. Growthresponses to brushing were seen several days after brushinghad ceased, noticeably in leaves which were barely visible atthe time of brushing. It is suggested that growth retardation of cauliflowers, lettuceand celery, induced by mechanical stress such as brushing mayprove valuable as a means of ‘conditioning’ theseedlings to withstand both the physical and physiological stresseswhich occur at and during transplanting. Brassica oleracea, cauliflower, Lactuca sativa L., lettuce, Apium graveolens L., celery, mechanical stress, shoot growth, root growth, chlorophyll     

Developmental Physiology of Sugar-beet: IV. EFFECTS OF GROWTH SUBSTANCES AND DIFFERENTIAL ROOT AND SHOOT TEMPERATURES ON SUBSEQUENT GROWTH

The effects of three growth substances, viz. indol-3yl-aceticacid (IAA), gibberellic acid (GA₃), and kinetin (KIN), and differentialshoot and root temperatures on growth of sugar-beet (Beta vulgarisL.) plants have been studied. IAA, GA₃, and KIN were applied in aqueous lanolin at differentconcentrations (50 ppm to 5000 ppm) to decapitated sugar-beetplants at the eight-leaf stage, one group also having alternateleaves removed. The growth substances significantly increasedthe dry weights of the plants when all the leaves were present,which was mainly explained by the large increase in roots. Thegrowth substances probably stimulated cambial activity and hencethe mobilization of substrates resulting in a bigger root whena relatively large leaf area existed. The failure of the plantsto respond to treatments following the removal of alternateleaves suggests that under such conditions the growth substanceshave hardly any major effect on the production of substrates;rather they influence growth by regulating the movement of substratesby altering the ‘sink strength’ if the supply ofsubstrates is not limiting. It could also be that the rootsproduce sufficient growth substances to maintain half the leavesat maximum expansion and maximum photosynthesis. Treatment withgrowth substances would therefore have little effect. When allthe leaves were present, they are limited by insufficient growthsubstances. All combinations of root and shoot temperatures of 17 and 25°C were imposed on plants decapitated at the eight-leafstage, one group also having each alternate leaf removed. Leaf8 expanded most at shoot and root temperature of 25 °C whereasother leaves had the largest areas at shoot and root temperatureof 17 °. When all the leaves were present root growth wasmaximal at shoot temperature of 17°C and root temperatureof 25 °C, but when alternate leaves were removed maximumroot growth occurred at shoot and root temperatures of 25 °C.Generally, a higher concentration of soluble carbohydrates wasfound in the roots and leaves when either the shoot or rootor both were kept at 17 °C. Concentrations of nitrogen,phosphorus, and potassium in different organs were less at 17°C than at higher shoot or root temperatures and decreasedwith age.     

Growth and Preferences for Ammonium or Nitrate Uptake by Barley in Relation to Root Termperature

Barley plants (Hordewn vulgare L. cv. Atem) were grown fromseed for 28 d in flowing solution culture, during which timeroot temperature was lowered decrementally to 5?C. Plants werethen subjected to root temperatures of 3, 5, 7, 9, 11, 13, 17or 25 ?C, with common air temperature of 25/15 ?C (day/night).Changes in growth, plant total N, and NO₃^– levels, andnet uptake of NH₄⁺ and NO₃^– from a maintained concentrationof 10 mmol m^–3 NH₄NO₃ were measured over 14 d. Dry matterproduction increased 6-fold with increasing root temperaturebetween 3–25 ?C. The growth response was biphasic followingan increase in root temperature. Phase I, lasting about 5 d,was characterized by high root specific growth rates relativeto those of the shoot, particularly on a fresh weight basis.During Phase I the shoot dry weight specific growth rates wereinversely related to root temperature between 3–13 ?C.Phase 2, from 5–14 d, was characterized by the approachtowards, and/or attainment of, balanced exponential growth betweenshoots and roots. Concentrations of total N in plant dry matterincreased with root temperature between 3–25 ?C, moreso in the shoots than roots and most acutely in the youngestfully expanded leaf (2?l–6?9% N). When N contents wereexpressed on a tissue fresh weight basis the variation withtemperature lessened and the highest concentration in the shootwas at 11 ?C. Uptake of N increased with root temperature, andat all temperatures uptake of NH₄⁺, exceeded that of NO₃^–,irrespective of time. The proportions of total N uptake over14 d absorbed in the form of NH₄⁺ were (%): 86, 91, 75, 77,76, 73, 77, and 80, respectively, at 3, 5, 7, 9, Il, 13, 17,and 25 ?C. At all temperatures the preference for NH₄⁺ overNO₃^– uptake increased with time. An inverse relationshipbetween root temperature (3–11 ?C) and the uptake of NH₄⁺as a proportion of total N uptake was apparent during PhaseI. The possible mechanisms by which root temperature limitsgrowth and influences N uptake are discussed. Key words: Hordeum vulgare, root temperature, ammonium, nitrate, ion uptake, growth rate     

不同水稻品系幼苗对砷（As）的耐性、吸收及转运

利用琼脂培养基模拟水稻生长的厌氧环境,研究了As对不同水稻品系幼苗生长的影响以及As在其体内的积累及转运特性.结果表明,不同浓度(0～4.0mg/L)的As对供试水稻品系根部干物质积累无显著影响(P>0.05).杂交稻与糯稻的地上部干物质积累随基质中As浓度的增加呈减小趋势,但低剂量的As(0.5mg/L)促进常规稻的生长.水稻地上部的As积累量随基质中As浓度的升高总体均呈增加趋势.水稻根系对As具有较强的吸收与累积能力.水稻根部As的积累量为156.31～504 03mg/kg,占总As含量的63.40～81.90%,远远高于其地上部As的积累量.相比于其它两个品系,糯稻的生物量积累高,耐性指数较大,根部及地上部对As的积累量较低,因此更适合种植在As污染土壤.     

Growth dynamics of root and shoot hydraulic conductance in seedlings of five neotropical tree species: scaling to show possible adaptation to differing light regimes

The dynamics of growth (shoot and root dry weights, surface areas, hydraulic conductances, and root length) were measured in seedlings of five neotropical tree species aged 4–16 months. The species studied included two light-demanding pioneers (Miconia argentea and Apeiba membranacea) and three shade-tolerant young- or old-forest species (Pouteria reticulata, Gustavia superba, and Trichilia tuberculata). Growth analysis revealed that shoot and root dry weights and hydraulic conductances and leaf area all increased exponentially with time. Alternative methods of scaling measured parameters to reveal differences that might explain adaptations to microsites are discussed. Scaling root conductance to root surface area or root length revealed a few species differences but nothing that correlated with adaptation to light regimes. Scaling of root surface area or root length to root dry weight revealed that pioneers produced significantly more root area and length per gram dry weight investment than shade-tolerant species. Scaling of root and shoot hydraulic conductances to leaf area and scaling of root conductance to root dry weight and shoot conductance to shoot dry weight also revealed that pioneers were significantly more conductive to water than shade-tolerant species. The advantages of scaling hydraulic parameters to leaf surface area are discussed in terms of the Ohm's law analogue of water flow in plants. Received: 24 March 1997 / Accepted: 17 November 1997     

Analysis of Dry Matter Partitioning in Dactylis glomerata during Vegetative Growth Using a Carbon Budget Model

The dry matter partitioning in vegetative plants of Dactylisglomerata was studied from experiments performed in controlledenvironments. Plants were grown hydroponically in growth chambers,at two constant temperatures (17 and 25 °C). In both experimentsthe root fraction decreased regularly with time, an effect thatwas more accentuated in the higher temperature regime. In orderto explain the change in dry matter partitioning, the experimentalshoot and root growth were analysed using a carbon budget modelwhich includes shoot and root maintenance requirements. Themodel predicts a relationship between the root specific growthrate and the product of shoot specific growth rate and shootto root dry weight ratio. In the range of experimental accuracy,this relationship was found to be linear at both temperatures,which should indicate that the partitioning coefficients andthe root maintenance coefficient remained constant during vegetativegrowth. The effect of temperature on the value of these coefficientscan be specified from a linear regression analysis. Between17 and 25 °C, the root maintenance coefficient increasedby about a factor of two, whereas the partitioning coefficientsdid not vary significantly. On the basis of these results, itwas shown that the decrease in root fraction during vegetativegrowth should be mainly attributed to the decrease in net specificactivity of shoots.Copyright 1994, 1999 Academic Press Dactylis glomerata L., vegetative growth, model, partitioning, root:shoot ratio, shoot specific activity, maintenance requirements     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)